Genetic counseling: Polydactyly and Syndactyly
Polydactyly and Syndactyly Contracting *What questions or concerns do you have? *What were you told about why you were referred? Medical and Family History *Medical history **How/when did they diagnose the polydactyly/syndactyly? **Is it bilateral? **Has she had X-rays or other imaging? Is this scheduled? **Pregnancy history - teratogen exposures, illness, womb anomalies **Birth history - any complications? **Hearing screen? Responses to sound? *Family history **Polydactyly/syndactyly? Other limb anomalies? **Cleft lip or palate? **Learning difficulties? Mental retardation? **Heart defects? Kidney abnormalities? **Skeletal abnormalities? Short stature? Other birth defects? Overview of Hand/Foot Abnormalities *Polydactyly **Presence of more than normal number of fingers or toes **Can vary from rudimentary finger or toe to fully developed extra digits *Syndactyly **Webbing or fusing of two or more fingers or toes **Varies from incomplete webbing of skin of two digits to complete untion of digits or fusion of bones and nails **Fusion can be connected by shared skin, bones, nerves, vessels, or nails *Polysyndactyly is presence of extra digits that are fused *Fetal development of digits **Limbs arise from small limb buds ***Upper limb bud appears 26-27 days after fertilization, lower limb bud 28-30 days ***Consists of mesenchymal core covered by epithelial tissue **Apical ectodermal ridge (AER) forms along anteroposterior surface ***Longitudinal growth of limb with pattern forming proximodistally and anteroposteriorly ***Homeobox genes and morphogen (possibly retinoic acid) provide information for cell growth and division **Separation of digits occurs due to programmed cell death in interdigital zones *Anything that disrupts patterning or programmed cell death can result in limb defect Syndactylies *Most are malformations except when associated with amniotic bands *Can be classified based on anatomic criteria **Syndactyly type I ***Cutaneous syndactyly of fingers 3 and 4 or toes 2 and 3 ***Can be bilateral in hands (50%) and feet (66%) ***Syndactyly of toes is four times more common than fingers ***Can be inherited as autosomal dominant trait ***About twice as common in males than in females **Syndactyly type II (synpolydactyly) ***Syndactyly of fingers 3 and 4 or toes 4 and 5 with partial or complete duplication of digit ***Can be variable, hand anomalies can be severe including clinodactyly ***Extra digit may have fused, forked, or broad metacarpals and metatarsals, complete or partial duplications or digit ***Incidence is uncertain, some autosomal dominant forms have been reported **Syndactyly type II ***Variable cutaneous or osseous syndactyly of fingers 3 to 5 ***Syndactyly might be complete or partial, nails may be fused ***Condition is rare **Syndactyly type IV (Haas type polysyndactyly) ***Complete cutaneous syndactyly of fingers and/or thumbs with a degree of polydactyly on radiography and a hypoplastic or triphalangeal thumb ***Hands often resemble "mitten" deformity ***Rarely seen as isolated defect, very rare with few families reported **Syndactyly type V ***Metacarpal and metatarsal fusion associated with variable degrees of syndactyly ***Usually involves digits 4 and 5 but can be variable ***Can be variable involvement within families ***Autosomal dominant and X-linked recessive families have been described ***Rare - only 10 families reported **Complete syndactyly ***Includes digits 2-5 and may include thumb also ***Usually seen with Apert syndrome (craniosynostosis) **Cenani-Lenz syndrome ***Syndactyly involving all elements of all digits, often with fusion of radius and ulna or tibia and fibula ***Hands and feet often appear as mass of digits ***Autosomal recessive inheritance **Preaxial syndactyly ***Failure of separation of preaxial digits of hands and feet ***Postaxial digits are relatively normal ***Lack of separation of thumb from finger 2 in hands, similar in feet ***Only reported in one family **Symbrachydactyly ***Shortening of phalanges and other elements of digits in association with cutaneous syndactyly ***Usually seen unilaterally, middle phalanges tend to be more severely affected ***Incidence estimated to be 1/32,000 Polydactylies *Usually manifest as extra digits or incomplete digits resulting in broad or bifid digit *Postaxial polydactyly (80% of cases) **Extra digit on ulnar or fibular side of limb **Type A postaxial polydactyly ***Digit usually consists of three phalanges and nail ***Extra digit is relatively well formed but some or all of elements may be reduced **Type B postaxial polydactyly ***Extra digit is represented by small conical projection or tag containing distal phalanx and nail on fifth digit ***10 times more common in African-Americans than Caucasians ***Unilateral in 2/3 of cases, affects left side twice as commonly as right ***Autosomal dominant inheritance with reduced penetrance *Preaxial polydactyly **Preaxial polydactyly type I ***Complete or partial duplication of a normal biphalangeal thumb ***Varies from extra phalanx to complete hypoplastic thumb ***May cause broadening of distal phalanx to triphalangeal thumb ***More common in males, most often unilateral, usually not familial ***Part of many malformation syndromes **Preaxial polydactyly type II (triphalangeal thumb) ***Opposable thumb with three phalanges ***Estimated incidence is 1/25,000 ***Usually sporadic, associated with prenatal hydantoin and thalidomide exposure, can be autosomal dominant **Preaxial polydactyly type III (polydactyly of an index finger) ***Duplication of the index finger with or without an additional biphalangeal or triphalangeal thumb ***Can be autosomal dominant or associated with genetic syndromes **Preaxial polydactyly type IV (polysyndactyly) ***Duplication of preaxial digits associated with syndactyly of the extra rays ***May see broadening of thumbs or six or seven toes ***Autosomal dominant with complete penetrance ***Sporadic cases occur in 1/10,000 births **Mirror hands and feet ***Polydactyly of hand or foot with appearance of mirror duplication around midline axis of arm or leg in absence of recognizable thumb or great toe ***Very rare with a few autosomal dominant cases but usually sporadic Treatment/Management Options *Diagnosed by external observation, X-ray, or ultrasound *Polydactyly **Can be corrected surgically to improve appearance and functioning **Usually done at 1 year of age so skeletal development is complete and accurate anatomic assessment can be done **May require reconstruction of any associated abnormalities in remaining digit **Cast and soft dressing may be used until healed *Syndactyly **Treatment aimed at maintaining and improving function with cosmetic benefits **Involves surgery and may require skin graft from groin area **Surgery usually done after 1 year and may be delayed as late as 18-24 months Genetic Etiology *Due to errors during fetal development, usually due to genetic defects **Can be isolated or associated with genetic syndrome **Isolated forms have autosomal dominant inheritance ***Variability in effects ***May be reduced penetrance in some cases **Some cases may be due to exposure to toxins or womb anomalies *Found as part of over 100 genetic syndromes Psychosocial Issues *Worry about what others will think - stigma of being different or having a child who is different *Worry about underlying cause or genetic syndrome *Guilt *Stress of taking child for doctors' visits, surgeries, therapies Resources *MUMS parent to parent matching :Phone: 1-877-336-5333 :Email: mums@netnet.net :Web:www.netnet.net/mums/ *Penn State Health and Disease Information :Web: www.hmc.psu.edu/healthinfo/pq/poly.htm *Specific resources and support groups available for genetic conditions References *"Hands and Feet." Human Malformations and Related Anomalies (1993). Oxford University Press, NY. *Novick, Car***"Polydactyly of the Foot." eMedicin***www.emedicing.com *"Polydactyly." Health Library. www.mercksource.com *"Polydactyly and Syndactyly." Penn State Health and Disease Information. www.hmc.psu.edu/healthinfo/ Notes The information in this outline was last updated in 2001. This material has been imported fom the wikibook "Genetic counseling"[ http://en.wikibooks.org/wiki/Genetic_counseling] under the GNU Free Documentation License.